This invention relates to a heat exchanger for use in a heat core or an oil cooler mounted in an automobile or for use as an evaporator or a condenser in an air conditioner, such as an automobile air conditioner, and, in particular, to a heat exchanger comprising a tube for flowing a heat transfer medium therethrough. This invention also relates to a method of manufacturing the above-mentioned heat exchanger by brazing a provisional or core assembly including the tube.
Generally, an internal fluid flowing through a pipe Is heat-exchanged with an external fluid outside the pipe. The internal fluid is called a heat transfer medium which transports heat or cold between two areas. On the other hand, the external fluid is a fluid, such as air and liquid, to be heated or cooled. In an air heating system, the heat transfer medium is a heat carrier such as steam or warm water which transports heat, while the external fluid is air. In an air cooling system, the heat transfer medium is called a refrigerant for cooling the air by the heat exchange therebetween. The air to be heated or cooled will often be referred to as heat exchange air.
A conventional heat exchanger comprises a pair of tanks, a plurality of tubes connecting those tanks to each other, and a plurality of fins arranged between and attached onto the tubes. Each of fins has an outer surface exposed to the external fluid to be heat-exchanged, for example, air in the air heating and/or cooling system.
The heat transfer medium flows through the tubes from one of the tanks to the other. The heat or the cold transported by the heat transfer medium is given to the air through the tube and the fins. Therefore, the tubes and the fins are often referred to as heat exchange tubes and heat exchange fins, respectively. The heat exchange fins serve to increase the area of a heat exchanging surface with which the air comes into contact so as to receive the heat or the cold.
The tubes and the fins are alternately arranged and pre-assembled with the tanks. Each of the tanks is composed of a combination of a tank base member and a tank cover member. Each tank base member is connected to open ends of the tubes. The preassembly of the tubes, fins, and tanks is subjected to a brazing process so as to fix or bond the tubes, fins, and tanks to one another to form an integral structure of the heat exchanger.
Each of the tubes comprises a pair of formed plates by pressing or molding. Each of the formed plates has a peripheral flange portion and a plurality of protrusions. Both of the formed plates have the protrusions. Each of the protrusions has a through-hole formed in a top end surface thereof.
When the preassembly is constructed, the formed plates are coupled to each other to form each tube. During carrying out the brazing process, flux is melted and flows into the interior of each tube through the through-holes and bonds or fixes the peripheral flange portions of both of the formed plates to each other so that the tube is sealed in a fluid-tight condition, as is already proposed in a copending U.S. patent application Ser. No. 505,850 filed on Jul. 24, 1995.
In the brazing process, a noncorrosive flux is used, which is available in commerce from ALCAN Corporation (Canada) under the trade name of "NOCOLOK FLUX".
However, In the above-mentioned technique, a brazing defect is often caused to occur if the brazed parts are not coated with a sufficient amount of the noncorrosive flux.